The present invention relates to a rack and pinion steering gear and, more particularly, to a rack and pinion steering gear having a low friction yoke assembly.
A known rack and pinion steering gear includes a pinion gear that is rotatably mounted in a housing and is connected with a steering wheel of a vehicle. A rack bar extends axially through the housing and has opposite end portions connected with steerable vehicle wheels. Gear teeth formed on the rack bar are disposed in meshing engagement with gear teeth on the pinion gear. A yoke assembly, including a yoke and a spring, is disposed in the housing to support and guide movement of the rack bar relative to the housing.
The yoke 210 of the known rack and pinion steering gear is shown in FIG. 6. An axially extending cavity 212 extends through the yoke 210 and intersects an upper surface 214 of the yoke 210. The axially extending cavity 212 forms diametrically opposite first and second support walls 216 and 218. The first and second support walls 216 and 218 support a spindle 220 that extends across the axially extending cavity 212 of the yoke 210. The length of the spindle 220 is approximately equal to the diameter of the yoke 210. The spindle 220 supports first and second roller assemblies 222 and 224 within the axially extending cavity 212. The first roller assembly 222 is near the first support wall 216 and the second roller assembly 224 is near the second support wall 218. Each of the first and second roller assemblies 222 and 224 include a roller 226 that is fixed to a bushing 228. Each roller 226 has a concave bearing surface 230 for contacting and supporting the rack bar 232. The first and second roller assemblies 222 and 224 rotate relative to the yoke 210 and the spindle 220 during axial movement of the rack bar 232.
During operation of this known rack and pinion steering gear, the yoke assembly may be subjected to both heat and high loads. The heat is produced by friction, generally between the rack bar 232 and the bearing surfaces 230 of the rollers 226 as the rack bar 232 moves over the rollers 226. A high load may occur, for example, when a vehicle hits a pothole in the road surface. The impact load of the vehicle tire with the pothole is transferred to the rack bar 232 through the vehicle tie rods. The rack bar 232, in turn, transfers a portion of the load to the yoke assembly. The load transferred to the yoke assembly should be absorbed by the spring that biases the yoke 210 against the rack bar 232. However, in the yoke assembly of the known rack and pinion steering gear, the load of the rack bar 232 on the rollers 226 creates a significant bending moment on the spindle 220. As a result, the load may cause the spindle 220 to bend in a location between the roller assemblies 222 and 224. When the spindle 220 bends, rotation of the first and second roller assemblies 222 and 224 may be impaired and increased friction and heat may develop between the rack bar 232 and the yoke assembly.
The present invention is a rack and pinion steering gear. The rack and pinion steering gear comprises a housing having an axially extending passage and a yoke bore that extends perpendicular to the axially extending passage and connects with the axially extending passage within the housing. A pinion gear having teeth is rotatably mounted in the housing. A rack bar extends through the axially extending passage of the housing and is movable relative to the pinion gear. The rack bar has teeth in meshing engagement with the teeth of the pinion gear. A yoke assembly is located in the yoke bore of the housing for at least partially supporting and guiding axial movement of the rack bar relative to the pinion gear. The yoke assembly comprises a yoke having first and second roller assemblies for contacting the rack bar and rotating during axial movement of the rack bar. A first spindle is fixed to the yoke and supports the first roller assembly and a second spindle is fixed to the yoke and supports the second roller assembly.